Tire molds often incorporate blades to form slots or grooves in the tread of a tire. These slots and grooves are typically referred to as sipes. The blades are typically thin metal strips of various lengths. The strips are typically straight but may include one or more bends and/or arcs depending on the shape of the sipe to be formed by the blade.
To mount the blade within a machined tire mold, slots are machined into the tire mold and the blade is inserted into the slots. Typically, the slot has a uniform depth and extends the entire length of the blade to provide the greatest amount of surface area for application of an adhesive, such as epoxy, to hold the blade within the slot. Since a single tire mold may include hundreds of slots, the time required to machine the slots is significant. Also, the labor involved in applying an adhesive to each blade before insertion is extensive. To that end, a self-locking blade has been recently developed to secure the blade within a slot without the need for the time consuming step of applying epoxy to the blade. The self-locking blade includes self-locking structures that expand outwardly to create an interference fit within the mold. To that end, grooves are formed in the tire mold to receive the self-locking structures. To allow the self-locking structure to expand, these grooves are undercut such that they have a trapezoidal profile with a base that is wider than the top opening of the groove, and sidewalls that slope inwardly from the base to the opening.
The self-locking structures include tendons that extend downward from the base of the blade. The tendons generally have a split configuration with a center portion that joins the split halves of the tendon and extends downward from the tendons. The tendons initially have a width less than the top opening within the groove to allow them to be easily inserted. To secure the blade, the blade is tapped with a hammer to collapse the center portion forcing it inward between the split halves. The collapsing center portion forces the split halves outward to fill the undercut portions of the groove.
While this blade improved over the prior method of securing blades with epoxy, the machining of the undercut grooves requires a five axis machine. Forming this undercut becomes even more difficult when using electric discharge machining (EDM). The use of EDM is attractive because of the speed with which slots may be formed using this technique. Therefore, a self-locking blade that does not require formation of an undercut groove within the tire mold is desirable.
Tire molds may also be constructed by casting the mold. In this process, the blades are attached by forming the mold around the blade. To that end, during the casting process, the blades are held in a pattern, and then molten mold material flows around the base of the blade. Taking advantage of this process, blades used in cast molds include notches on the side of the blade base below the top surface of the mold so that the molten material flows into these notches and positively stops the blade from being pulled out. It will be appreciated that this type of blade cannot be used in a machined slot. Therefore, it is desirable to have a self-locking blade that can be used in both a machined mold and a cast mold.